Low Density Parity Check (LDPC) Encoded Higher Order Modulation

ABSTRACT

A method and apparatus is disclosed to map a sequence of data to Quadrature Amplitude Modulation (QAM) constellation symbols. The method and apparatus encodes only a portion of the sequence of data and leaves a remaining portion of the sequence of data unencoded. The encoded portion of the sequence of data and the remaining unencoded portion of the sequence of data are then mapped into modulation symbols of the QAM constellation. The encoded portion of the sequence of data selects subsets of the QAM constellation, and the remaining unencoded portion of the sequence of data determines a specific modulation symbol within each subset of the QAM constellation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentAppl. No. 60/988,644, filed Nov. 16, 2007, entitled “Low Density ParityCheck Mapping,” which is incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is generally related to communication systems.More particularly, the present invention is related to mapping asequence of data to a Quadrature Amplitude Modulation (QAM)constellation.

2. Related Art

Quadrature amplitude modulation (QAM) is a digital modulation schemethat conveys data by modulating the amplitude and phase of a sinusoidalcarrier signal. A constellation diagram depicts the employed set ofdiscrete modulation values in the complex (or Argand) plane, in whichtypically the x-axis represents real parts and the y-axis representsimaginary parts. The points of the constellation diagram are usuallyreferred to as the modulation symbols that comprise the modulationalphabet. In a QAM scheme, the constellation points are often arrangedin a square grid with equal vertical and horizontal spacing, althoughother configurations are possible. The number of points on theconstellation diagram for a QAM scheme is usually a power of two, suchas two, four, or eight, to provide some examples. Some of the mostcommon number of points on the constellation diagram are sixteen pointsrepresenting a 16-QAM, sixty four points representing a 64-QAM, onehundred twenty eight points representing a 128-QAM, and two hundredfifty six points representing a 256-QAM. By moving to a higher-orderconstellation, such as 1024-QAM to provide an example, more bits persymbol can be transmitted. However, for a given average energy persymbol the constellation points in a higher-order constellation must becloser together. This makes discrimination between the modulationsymbols more susceptible to noise and other signal corruptions, and thuscan result in a higher error rate.

Commonly, the reliability of symbol detection in the receiver can beincreased by restricting the permitted sequence of QAM symbols by anerror correction code. In this case, an encoder adds redundancies to thesequence of bits, which are then mapped into QAM symbols. A receiver canthen exploit the redundancies to improve the correct determination ofthe transmitted sequence of modulation symbols. Among variouserror-correction codes, low density parity check (LDPC) codes areparticularly well suited for achieving performance very close to thecapacity of a given communication channel. However, very long LDPC codesrequiring complex encoders and decoders are needed to obtain goodresults for higher-order QAM, if all constellation bits are encoded.

Thus, there is a need for an apparatus and/or a method to encode datainto higher-order QAM symbols by a LDPC code that overcomes theshortcomings described above. Further aspects and advantages of thepresent invention will become apparent from the detailed descriptionthat follows.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings illustrate the present invention and, togetherwith the description, further serve to explain the principles of thepresent invention and to enable one skilled in the pertinent art to makeand use the present invention.

FIG. 1 illustrates a block diagram of a communications environmentaccording to an exemplary embodiment of the present invention.

FIG. 2 illustrates a block diagram of a communications transmitter usedin the communications environment according to an exemplary embodimentof the present invention.

FIG. 3A illustrates a block diagram of a communications encoder used inthe communications transmitter according to an exemplary embodiment ofthe present invention.

FIG. 3B illustrates an example block diagram of an encoding moduleaccording to an exemplary embodiment of the present invention.

FIG. 4 illustrates a 256-Quadrature Amplitude Modulation (QAM)constellation according to an exemplary embodiment of the presentinvention.

FIG. 5 illustrates another 256-QAM constellation, a 1024-QAMconstellation, and a 4096-QAM constellation according to an exemplaryembodiment of the present invention.

FIG. 6 is a flowchart of exemplary operational steps of thecommunications transmitter used in the communications environmentaccording to an aspect of the present invention.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers generallyindicate identical, functionally similar, and/or structurally similarelements. The drawing in which an element first appears is indicated bythe leftmost digit(s) in the reference number.

DETAILED DESCRIPTION OF THE INVENTION

Overview

The present invention relates to mapping a sequence of data toQuadrature Amplitude Modulation (QAM) constellation symbols by encodingonly a portion of the sequence of data and leaving a remaining portionof the sequence of data unencoded. The encoded portion of the sequenceof data and the remaining unencoded portion of the sequence of data arethen mapped into modulation symbols of the QAM constellation. Theencoded portion of the sequence of data selects subsets of the QAMconstellation, and the remaining unencoded portion of the sequence ofdata determines specific modulation symbols within the selected subsetsof the QAM constellation.

The following Detailed Description refers to accompanying drawings toillustrate exemplary embodiments consistent with the present invention.References in the Detailed Description to “one exemplary embodiment,”“an exemplary embodiment,” “an example exemplary embodiment,” etc.,indicate that the exemplary embodiment described may include aparticular feature, structure, or characteristic, but every exemplaryembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same exemplary embodiment. Further, when a particularfeature, structure, or characteristic is described in connection with anexemplary embodiment, it is within the knowledge of those skilled in therelevant art(s) to effect such feature, structure, or characteristic inconnection with other exemplary embodiments whether or not explicitlydescribed.

The exemplary embodiments described herein are provided for illustrativepurposes, and are not limiting. Other exemplary embodiments arepossible, and modifications may be made to the exemplary embodimentswithin the spirit and scope of the present invention. Therefore, theDetailed Description is not meant to limit the present invention.Rather, the scope of the present invention is defined only in accordancewith the following claims and their equivalents.

The following Detailed Description of the exemplary embodiments will sofully reveal the general nature of the present invention that otherscan, by applying knowledge of those skilled in relevant art(s), readilymodify and/or adapt for various applications such exemplary embodiments,without undue experimentation, without departing from the spirit andscope of the present invention. Therefore, such adaptations andmodifications are intended to be within the meaning and plurality ofequivalents of the exemplary embodiments based upon the teaching andguidance presented herein. It is to be understood that the phraseologyor terminology herein is for the purpose of description and not oflimitation, such that the terminology or phraseology of the presentspecification is to be interpreted by those skilled in relevant art(s)in light of the teachings herein.

Communications Environment

FIG. 1 illustrates a block diagram of a communications environmentaccording to an exemplary embodiment of the present invention. Thecommunications environment 100 includes a communications transmitter 102to transmit a sequence of data 150 as received from one or morecommunications transmitter user devices to a communications receiver 106via a communications channel 104. The one or more communicationstransmitter user devices may include, but are not limited to, personalcomputers, data terminal equipment, telephony devices, broadband mediaplayers, personal digital assistants, software applications, or anyother device capable of transmitting or receiving data. Thecommunications transmitter 102 provides a transmitted signal 152 basedon the sequence of data 150.

The transmitted signal 152 passes through the communications channel 104to provide a received signal 154. The communications channel 104 mayinclude, but is not limited to, a microwave radio link, a satellitechannel, a fiber optic cable, a hybrid fiber optic cable system, or acopper cable to provide some examples. The communications channel 104contains a propagation medium that the transmitted signal 152 passesthrough before reception by the communications receiver 106. Thepropagation medium of the communications channel 104 may introduceinterference and/or distortion into the transmitted signal 152 causingthe received signal 154 to differ significantly from the transmittedsignal 152. For example, noise such as, but not limited to, thermalnoise, burst noise, impulse noise, interference, signal strengthvariations known as fading, phase shift variations, to provide someexamples, may introduce the interference and/or the distortion into thetransmitted signal 152.

The communications receiver 106 observes the received signal 154 as itpasses through the communications channel 104. The communicationsreceiver 106 determines a most-likely transmitted sequence of modulationsymbols of the transmitted signal 152 and data bits encoded therein toprovide a sequence of recovered data 156. The sequence of recovered data156 is provided to one or more receiver user devices such as, but notlimited to, personal computers, data terminal equipment, telephonydevices, broadband media players, personal digital assistants, softwareapplications, or any other device capable of transmitting or receivingdata.

Communications Transmitter

FIG. 2 illustrates a block diagram of a communications transmitter usedin the communications environment according to an exemplary embodimentof the present invention. The communications transmitter 102 includes acommunications encoder 202, a symbol mapper 204, and a modulator 206.The communications encoder 202 provides a sequence of encoded data 250based upon the sequence of data 150.

The sequence of encoded data 250 is segmented into N-bit patternsreferred to as symbol labels. The symbol mapper 204 assigns to eachsymbol label a corresponding modulation symbol from an 2^(N)-QAMconstellation in accordance with a specific mapping scheme to provide asequence of modulated data 252. In an exemplary embodiment, the symbolmapper 204 maps four-bit symbol labels into their corresponding symbolsfrom a 16-QAM constellation. In another, the symbol mapper 204 mapsfive-bit symbol labels into their corresponding symbols from a 32-QAMconstellation. In a further exemplary embodiment, the symbol mapper 204maps six-bit symbol labels into their corresponding symbols from a32-QAM constellation. However, these examples are not limiting; thoseskilled in the relevant art(s) may segment the sequence of encoded data250 into symbol labels of different length.

The symbol mapper 204 may map the symbol labels into their correspondingsymbols according to a Gray mapping scheme. An exemplary embodiment ofthe Gray mapping scheme for the 16-QAM modulation is shown below:

Gray mapping scheme for the 16-QAM modulation A

 0000 B

 0100 C

 1100 D

 1000 E

 0001 F

 0101 G

 1101 H

 1001 I

 0011 J

 0111 K

 1111 L

 1011 M

 0010 N

 0110 O

 1110 P

 1010As shown in the table above, the Gray mapping scheme for the 16-QAMmodulation may map each of the four-bit symbol labels into theircorresponding symbols from the 16-QAM constellation. For example, asymbol label 0000 may be mapped to a first symbol A by the symbol mapper204. Likewise, a symbol label 0001 may be mapped to a second symbol E bythe symbol mapper 204. Similarly, a symbol label 1010 may be mapped to asixteenth symbol P by the symbol mapper 204.

The modulator 206 modulates a carrier frequency with the sequence ofmodulated data 252 to provide the transmitted signal 152. The modulator206 modulates the carrier frequency with the sequence of modulated data252 to transfer the sequence of modulated data 252 over thecommunications channel 104 via the transmitted signal 152. In anexemplary embodiment, the modulator 206 is optional; the communicationstransmitter 102 may directly transmit the sequence of modulated data 252as the transmitted signal 152.

Communications Encoder

FIG. 3A illustrates a block diagram of a communications encoder used inthe communications transmitter according to an exemplary embodiment ofthe present invention. The communications encoder 202 includes a firstencoding module 302, a bit splitter module 304, a second encoding module306, and a bit combiner module 308. The first encoding module 302provides a sequence of encoded data 350 based upon the sequence of data150. The first encoding module 302 encodes the sequence of data 150 toprovide the sequence of encoded data 350 using one or more encodingalgorithms. The sequence of encoded data 350 may include a length of pbits, where p includes one or more parity bits.

The one or more encoding algorithms may include an outer encodingalgorithm to provide the one or more parity bits and/or an innerencoding algorithm to provide the one or more parity bits. For example,the first encoding module 302 may encode the sequence of data 150 usingan outer encoding algorithm, such as the Bose-Chaudhuri-Hocquenghem(BCH) code or the well known Reed Solomon code to provide some examples,and/or an inner encoding algorithm, such as the Digital VideoBroadcasting-Satellite-Second Generation Low Density Parity Check(DVB-S2 LDPC) code to provide an example. The BCH Code and the DVB-S2LDPC code are further described in the Digital Video Broadcasting (DVB);Second generation framing structure, channel coding and modulationsystems for Broadcasting, Interactive Services, News Gathering and otherbroadband satellite applications, ESTI Reference No. ETSI EN 302 307V1.1.2 (2006-06), which is incorporated by reference herein in itsentirety. However, these example are not limiting, those skilled therelevant art(s) may implement any other suitable outer encodingalgorithm and/or inner encoding algorithm differently in accordance withthe teachings herein without departing from the spirit and scope of thepresent invention. Alternatively, the first encoding module 302 mayencode the sequence of data 150 using only the outer encoding algorithm.In an exemplary embodiment, the first encoding module 302 is optional;the bit splitter module 304 may directly receive the sequence of data150.

The bit splitter module 304 provides a sequence of unencoded data 352and a sequence of pre-encoded data 354 based upon the sequence of data150 or the sequence of encoded data 350. The bit splitter module 304parses or separates the sequence of data 150 or the sequence of encodeddata 350 into the sequence of unencoded data 352 and the sequence ofpre-encoded data 354. The sequence of unencoded data may include alength of m bits and the sequence of pre-encoded data 354 may include alength of p−m bits. In other words, the bit splitter module 304separates the sequence of data 150 or the sequence of encoded data 350into a first bit portion of m bits representing the sequence ofunencoded data 352 and a second bit portion of p−m bits representing thesequence of pre-encoded data 354. For example, the sequence of data 150or the sequence of encoded data 350 may include a sequence of 122,992bits. In this example, the sequence of unencoded data 352 may include asequence of 64,800 bits and the pre-encoded block of information 350 mayinclude a sequence of 58,192 bits. As another example, the sequence ofdata 150 or the sequence of encoded data 350 may include a sequence of30,432 bits. In this example, the sequence of unencoded data 352 mayinclude a sequence of 16,200 bits and the pre-encoded block ofinformation 350 may include a sequence of 14,232 bits.

The second encoding module 306 provides a sequence of encoded data 356based upon the sequence of pre-encoded data 354. The second encodingmodule 306 encodes the sequence of pre-encoded data 354 to provide thesequence of encoded data 356 using one or more encoding algorithms. Thesequence of encoded data 356 may include a length of p−m+r bits, where rrepresents one or more parity bits created by the second encoding module306. The second encoding module 306 may represent a systematic encoder,and/or a non-systematic encoder. For example, the second encoding module306, when implemented as the systematic encoder, provides the sequenceof encoded data 356 including the sequence of pre-encoded data 354 and radditional parity bits. Alternately, the second encoding module 306,when implemented as the non-systematic encoder, provides the sequence ofencoded data 356 that does not include the p−m bits of the sequence ofpre-encoded data 354. Rather, the non-systematic encoder provides a setof bits that is not embedded with the sequence of pre-encoded data 354.When implemented as either the systematic encoder or the non-systematicencoder, the second encoding module 306 encodes the p−m bits of thesequence of pre-encoded data 354 to provide p−m+r bits representing thesequence of encoded data 356. For example, the second encoding module306 may encode sequence of 58,192 bits representing the sequence ofpre-encoded data 354 to provide of sequence of 64,800 bits representingthe sequence of encoded data 356. As another example, the secondencoding module 306 may encode sequence of 14,232 bits representing thesequence of pre-encoded data 354 to provide sequence of 16,200 bitsrepresenting the sequence of encoded data 356. The second encodingmodule 306 is described in further detail below.

The bit combiner module 308 provides the sequence of encoded data 250based upon the sequence of unencoded data 352 and the sequence ofencoded data 356. The bit combiner module 308 combines the sequence ofunencoded data 352 and the sequence of encoded data 356 to provide thesequence of encoded data 250. More specifically, the bit combiner module308 combines a first bit portion of the sequence of unencoded data 352and a second bit portion of the sequence of encoded data 356 to providethe sequence of encoded data 250.

In an exemplary embodiment, the m unencoded bits are passed in M_(msb)bit increments to the bit combiner module 308. Likewise, the p−m+rencoded bits are passed in M_(lsb) bit increments to the bit combinermodule 308. For example, the bit combiner module 308 may provide thesequence of encoded data 250 at a rate of eight bits per symbol byreceiving a sequence of four-bit increments from the sequence ofunencoded data 352 and a sequence of four-bit increments from thesequence of encoded data 356. In this example, the bit combiner module308 combines the four-bit increments of the sequence of unencoded data352 and the four-bit increments of the sequence of encoded data 356 suchthat the sequence of encoded data 250 corresponds to modulation symbolsof a 256-QAM constellation. Alternatively, the bit combiner module 308may provide the sequence of encoded data 250 at the rate of eight bitsper symbol by receiving a sequence of two-bit increments from thesequence of unencoded data 352 and a sequence of six-bit increments fromthe sequence of encoded data 356. In this example, the bit combinermodule 308 combines the two-bit increments of the sequence of unencodeddata 352 and the six-bit increments of the sequence of encoded data 356such that the sequence of encoded data 250 corresponds to modulationsymbols of the 256-QAM constellation.

As another example, the bit combiner module 308 may provide the sequenceof encoded data 250 at the rate of ten bits per symbol by receiving asequence of four-bit increments from the sequence of unencoded data 352and a sequence of six-bit increments from the sequence of encoded data356. In this example, the bit combiner module 308 combines the four-bitincrements of the sequence of unencoded data 352 and the six-bitincrements of the sequence of encoded data 356 such that the sequence ofencoded data 250 corresponds to modulation symbols of a 1024-QAMconstellation.

As a further example, the bit combiner module 308 may provide thesequence of encoded data 250 at the rate of twelve bits per symbol byreceiving a sequence of six-bit increments from the sequence ofunencoded data 352 and a sequence of six-bit increments from thesequence of encoded data 356. In this example, the bit combiner module308 combines the six-bit increments of the sequence of unencoded data352 and the six-bit increments of the sequence of encoded data 356 suchthat the sequence of encoded data 250 corresponds to modulation symbolsof a 4096-QAM constellation.

Encoding Module

FIG. 3B illustrates an example block diagram of the encoding module 306according to an exemplary embodiment of the present invention. Asdiscussed above, the second encoding module 306 encodes the sequence ofpre-encoded data 354 to provide the sequence of encoded data 356 usingthe one or more encoding algorithms. The second encoding module 306includes an outer encoding module 310, an inner encoding module 312, andan interleave module 314. The sequence of encoded data 356 may include alength of p−m+r bits, where r may include one or more parity bits,r_(o), provided by an outer encoding algorithm and/or one or more paritybits, r_(i), provided by an inner encoding algorithm.

The outer encoding module 310 encodes the sequence of pre-encoded data354 to provide a sequence of outer encoded data 358 using a firstencoding algorithm. The sequence of outer encoded data 358 may include alength of p−m+r_(o) bits, where r_(o) represents one or more parity bitsprovided by the outer encoding module 310. In an exemplary embodiment,the outer encoding module 310 encodes the sequence of pre-encoded data354 according to the BCH code. However, this example is not limiting,those skilled the relevant art(s) may implement any other suitableencoding algorithm differently in accordance with the teachings hereinwithout departing from the spirit and scope of the present invention.For example, the outer encoding module 310 may encode the sequence of58,192 bits representing the sequence of pre-encoded data 354 to providethe sequence of outer encoded data 358 including the sequence of 58,320bits using the BCH code. In this example, the outer encoding module 310creates a sequence of 128 parity bits for the sequence of outer encodeddata 358. As another example, the outer encoding module 310 may encodethe sequence of 14,232 bits representing the sequence of pre-encodeddata 354 to provide the sequence of outer encoded data 358 including thesequence of 14,400 bits using the BCH code. In this example, the outerencoding module 310 creates 168 parity bits for the sequence of outerencoded data 358.

The inner encoding module 312 encodes the sequence of outer encoded data358 to provide a sequence of inner encoded data 360 using a secondencoding algorithm. The sequence of inner encoded data 360 may includeincluding a length of p−m+r_(o)+r_(i) bits, where r_(i) represents oneor more parity bits provided by the inner encoding module 312. In anexemplary embodiment, the inner encoding module 312 encodes the sequenceof outer encoded data 358 according to the DVB-S2 LDPC code. However,this example is not limiting, those skilled the relevant art(s) mayimplement any other suitable encoding algorithm differently inaccordance with the teachings herein without departing from the spiritand scope of the present invention.

For example, the inner encoding module 312 may encode the sequence of58,320 bits representing the sequence of outer encoded data 358 toprovide the sequence of inner encoded data 360 including sequence of64,800 bits using the DVB-S2 LDPC code. In this example, the innerencoding module 312 creates a sequence of 6,480 parity bits for thesequence of inner encoded data 360. As another example, the innerencoding module 312 may encode the sequence of 14,400 bits representingthe sequence of outer encoded data 358 to provide the sequence of innerencoded data 360 including the sequence of 16,200 bits using the DVB-S2LDPC code. In this example, the inner encoding module 312 creates 1800parity bits for the sequence of inner encoded data 360.

The interleave module 314 interleaves the sequence of inner encoded data360 to provide the sequence of encoded data 356. The p−m+r encoded bitsare passed in M_(lsb) bit increments by the interleave module 314 viathe sequence of encoded data 356 to the bit combiner module 308. Theconfiguration of the interleave module 314 for the 256-QAM, 1024-QAM,and the 4096-QAM is shown below:

COLUMNS ROWS 256-QAM 4 unencoded bits per symbol 4 encoded bits persymbol 4 $\frac{\left( {p - m + r_{o} + r_{i}} \right)}{4}$ 256-QAM 2unencoded bits per symbol 6 encoded bits per symbol 6$\frac{\left( {p - m + r_{o} + r_{i}} \right)}{6}$ 1024-QAM 6 unencodedbits per symbol 4 encoded bits per symbol 4$\frac{\left( {p - m + r_{o} + r_{i}} \right)}{4}$ 1024-QAM 4 unencodedbits per symbol 6 encoded bits per symbol 6$\frac{\left( {p - m + r_{o} + r_{i}} \right)}{6}$ 4096-QAM 8 unencodedbits per symbol 4 encoded bits per symbol 4$\frac{\left( {p - m + r_{o} + r_{i}} \right)}{4}$ 4096-QAM 6 unencodedbits per symbol 6 encoded bits per symbol 6$\frac{\left( {p - m + r_{o} + r_{i}} \right)}{6}$ 4096-QAM 4 unencodedbits per symbol 8 encoded bits per symbol 8$\frac{\left( {p - m + r_{o} + r_{i}} \right)}{8}$As shown in the table above, the interleave module 314 may write thesequence of inner encoded data 360 column-wise and read the sequence ofinner encoded data 360 row-wise to provide the sequence of encoded data356. For example, the interleave module 314 may write the sequence ofinner encoded data 360 into four columns including

$\frac{\left( {p - m + r_{o} + r_{i}} \right)}{4}$

total bits per column. In this example, the interleave module 314 readsthe sequence of inner encoded data 360 from

$\frac{\left( {p - m + r_{o} + r_{i}} \right)}{4}$

rows including four-bits per row to provide the sequence of encoded data356 representing the 256-QAM constellation.

Those skilled in the relevant art(s) will recognize that the secondencoding module 306 need not include the outer encoding module 310, theinner encoding module 312, and/or the interleave module 314 withoutdeparting from the spirit and scope of the present invention. Forexample, the second encoding module 306 may include only the innerencoding module 312. In this example, the inner encoding module 312directly encodes the sequence of pre-encoded data 354 to provide thesequence of encoded data 356.

The DVB-S2 LDPC code is primarily used to encode low densityconstellations such as Quadrature Phase Shift Keyed (QPSK), 8-PhaseShift Keyed (PSK), 16 Asymmetric Phase Shift Keyed (APSK) and/or 32 APSKconstellations to provide some examples. However, the partitioning ofthe sequence of encoded data 350 into the sequence of unencoded data 352and the sequence of pre-encoded data 354 followed by recombining thesequence of unencoded data 352 and the sequence of encoded data 356allows for the use of the DVB-S2 LDPC code for higher densityconstellations, such as 256-QAM, 1024-QAM, and/or 4096-QAM to providesome examples. In other words, the second encoding module 306 may reuseone or more encoding algorithms engineered to provide low densityconstellations in providing for higher density constellations.

QAM Constellations

FIG. 4 illustrates a 256-Quadrature Amplitude Modulation (QAM)constellation according to an exemplary embodiment of the presentinvention. From the discussion above, the sequence of unencoded data 352may include a sequence of four-bit increments and the sequence ofencoded data 356 may include a sequence of four-bit increments. Thecommunications encoder 202 may provide the sequence of encoded data 250representing one or more of the 256 modulation symbols of the 256-QAMconstellation by receiving the sequence of four-bit increments from thesequence of unencoded data 352 and the sequence of four-bit incrementsfrom the sequence of encoded data 356.

As shown in FIG. 4, the sequence of four-bit increments from thesequence of unencoded data 352 represent a corresponding one of sixteensubsets of constellation points, denoted as “A” through “P”, of the256-QAM constellation while the sequence of four-bit increments from thesequence of encoded data 356 represent a corresponding one of thesixteen modulation symbols, denoted as “a” through “p”, within thecorresponding one of the sixteen subsets of constellation points. Forexample, when the symbol mapper 204 maps the four-bit symbol labels intothe 16-QAM modulation symbols according to the Gray mapping scheme, thenthe constellation point “Ad” represents the symbol label (0000, 1000).Likewise, the constellation point “Mm” represents the symbol label(0010, 0010). Alternatively, the sequence of four-bit increments fromthe sequence of encoded data 356 represent a corresponding one ofsixteen subsets of constellation points, denoted as “a” through “p”, ofthe 256-QAM constellation while the sequence of four-bit increments fromthe sequence of unencoded data 352 represent a corresponding one of thesixteen modulation symbols, denoted as “A” through “P”, within thecorresponding one of the sixteen subsets of constellation points.

Although the sixteen subsets of constellation points are not protectedby coding, these sixteen subsets of constellation points have a largerminimum Euclidean distance of separation when compared to the sixteenmodulation symbols within each of the sixteen subsets of constellationpoints, due to set partitioning. For example, the constellation point“Am” and the constellation point “Bm” have a larger minimum Euclideandistance of separation when compared to the constellation point “Am” andthe constellation point “An”. However, the least significant bits of theconstellation point “Am”, namely “m” and the least significant bits ofthe constellation point “An”, namely “n” are protected by coding.

FIG. 5 illustrates another 256-QAM constellation, a 1024-QAMconstellation, and a 4096-QAM constellation according to an exemplaryembodiment of the present invention. From the discussion above, the bitcombiner module 308 may provide the sequence of encoded data 250 at arate of eight, ten, or twelve bits per symbol label such that thesequence of encoded data 250 represents one or more of the 256modulation symbols of the 256-QAM constellation, one or more of the 1024modulation symbols of the 1024-QAM constellation, or one or more of the4096 modulation symbols of the 4096-QAM constellation, respectively. Thesequence of unencoded data 352 may be provided at a rate of two, four,or six-bit increments and the sequence of encoded data 356 may beprovide at a rate of four-bit increments.

As shown in FIG. 5, the sequence of two-bit increments from the sequenceof unencoded data 352 represent a corresponding one of four subsets ofconstellation points of the 256-QAM constellation while the sequence ofsix-bit increments from the sequence of encoded data 356 represent acorresponding one of the sixty-four modulation symbols, denoted as b₀through b₆₃, within the corresponding one of the four subsets ofconstellation points. Likewise, the sequence of four-bit increments fromthe sequence of unencoded data 352 represent a corresponding one ofsixteen subsets of constellation points of the 1024-QAM constellationwhile the sequence of six-bit increments from the sequence of encodeddata 356 represent a corresponding one of the sixty-four modulationsymbols, denoted as b₀ through b₆₃, within the corresponding one of thesixteen subsets of constellation points. Similarly, the sequence ofsix-bit increments from the sequence of unencoded data 352 represent acorresponding one of sixty-four subsets of constellation points of the4096-QAM constellation while the sequence of six-bit increments from thesequence of encoded data 356 represent a corresponding one of thesixty-four modulation symbols, denoted as b₀ through b₆₃, within thecorresponding one of the sixty-four subsets of constellation points.

Operational Control Flow of the Communications Transmitter

FIG. 6 is a flowchart 600 of exemplary operational steps of thecommunications transmitter used in the communications environmentaccording to an aspect of the present invention. Rather, it will beapparent to persons skilled in the relevant art(s) from the teachingsherein that other operational control flows are within the scope andspirit of the present invention. The following discussion describes thesteps in FIG. 6.

At step 602, the operational control flow starts. The operational flowcontrol proceeds to step 604.

At step 604, the operational control flow encodes a sequence of data,such as the sequence of data 150 to provide an example, using one ormore first encoding algorithms to provide a sequence of encoded data,such as the sequence of encoded data 350 to provide an example. Thesequence of encoded data may include a length of p bits, where pincludes one or more parity bits. The one or more first encodingalgorithms may include an outer encoding algorithm to provide the one ormore parity bits and/or an inner encoding algorithm to provide the oneor more parity bits.

For example, the operational control flow may encode the sequence ofdata in its entirety using an outer encoding algorithm, such as theBose-BCH code or the well known Reed Solomon code to provide someexamples, and/or an inner encoding algorithm, such as the DVB-S2 LDPCcode to provide an example. Alternatively, the operational control flowmay encode the sequence of data in its entirety using only the outerencoding algorithm. In an exemplary embodiment, step 604 is optional;step 606 may directly receive the sequence of data.

At step 606, the operational control flow parses or separates thesequence of encoded data from step 604 or the sequence of data from step604 into a first portion of data, such as the sequence of pre-encodeddata 354 to provide an example, and a second portion, such as thesequence of unencoded data 352 to provide an example. The first portionof data may include a length of p−m bits and the second portion of datamay include a length of p bits.

At step 608, the operational control flow encodes the p−m bits of thefirst portion of data from step 606 to provide an encoded first portionof data, such as the sequence of encoded data 356 to provide an example,of length p−m+r_(o)+r_(i) bits using one or more second encodingalgorithms. The one or more second encoding algorithms may include anouter encoding algorithm to provide the r_(o) parity bits and/or aninner encoding algorithm to provide the r_(i) parity bits.

For example, the operational control flow may encode the first portionof data from step 606 in its entirety using an inner encoding algorithm,such as the DVB-S2 LDPC code to provide an example. Alternatively, theoperational control flow may encode the first portion of data from step606 in its entirety using the outer encoding algorithm, such as theBose-BCH code or the well known Reed Solomon code to provide someexamples, and/or the inner encoding algorithm, such as the DVB-S2 LDPCcode to provide an example.

The operational control flow may additionally interleave the firstportion of data from step 606 after encoding by the inner encodingalgorithm and/or the outer encoding algorithm.

At step 610, the operational control flow combines a part of the encodedfirst portion of data from step 608 and a part of the second portion ofdata from step 606 to provide a sequence of encoded data, such as thesequence of encoded data 250 to provide an example.

The operational control flow combines M_(lsb) bit increments of thep−m+r encoded bits of the encoded first portion of data from step 608and M_(msb) bit increments of the m unencoded bits of the second portionof data from step 606 to provide the sequence of encoded data. Forexample, the operational control flow may provide the sequence ofencoded data at a rate of eight bits per symbol by receiving a sequenceof four-bit increments from the second portion of data from step 606 anda sequence of four-bit increments from the encoded first portion of datafrom step 608. In this example, the operational control flow combinesthe four-bit increments of the second portion of data from step 606 andthe four-bit increments of the encoded first portion of data from step608 such that the sequence of encoded data corresponds to modulationsymbols of a 256-QAM constellation. Alternatively, the operationalcontrol flow may provide the sequence of encoded data at the rate ofeight bits per symbol by receiving a sequence of two-bit increments fromthe second portion of data from step 606 and a sequence of six-bitincrements from the encoded first portion of data from step 608. In thisexample, the operational control flow combines the two-bit increments ofthe second portion of data from step 606 and the six-bit increments ofthe encoded first portion of data from step 608 such that the sequenceof encoded data corresponds to modulation symbols of the 256-QAMconstellation.

As another example, the operational control flow may provide thesequence of encoded data at the rate of ten bits per symbol by receivinga sequence of four-bit increments from the second portion of data fromstep 606 and a sequence of six-bit increments from the encoded firstportion of data from step 608. In this example, the operational controlflow combines the four-bit increments of the second portion of data fromstep 606 and the six-bit increments of the encoded first portion of datafrom step 608 such that the sequence of encoded data corresponds tomodulation symbols of a 1024-QAM constellation.

As a further example, the operational control flow may provide thesequence of encoded data at the rate of twelve bits per symbol byreceiving a sequence of six-bit increments from the second portion ofdata from step 606 and a sequence of six-bit increments from the encodedfirst portion of data from step 608. In this example, the operationalcontrol flow combines the six-bit increments of the second portion ofdata from step 606 and the six-bit increments of the encoded firstportion of data from step 608 such that the sequence of encoded datacorresponds to modulation symbols of a 4096-QAM constellation.

At step 612, the operational control flow segments the sequence ofencoded data from step 610 into N-bit patterns referred to as symbollabels. For example, the operational control flow may segment thesequence of encoded data from step 610 into four-bit, five-bit, and/orsix-bit patterns.

At step 614, the operational control flow assigns to each symbol labelfrom step 612 a corresponding modulation symbol from an 2^(N)-QAMconstellation in accordance with a specific mapping scheme to provide asequence of modulated data, such as the sequence of modulated data 252to provide an example. In an exemplary embodiment, the symbol mapper 204maps four-bit symbol labels into their corresponding symbols from a16-QAM constellation. In another, the operational control flow mapsfive-bit symbol labels from step 612 into their corresponding symbolsfrom a 32-QAM constellation. In a further exemplary embodiment, theoperational control flow maps six-bit symbol labels from step 612 intotheir corresponding symbols from a 64-QAM constellation. In a yetfurther exemplary embodiment, the operational control flow may map thesymbol labels from step 612 into their corresponding symbols accordingto the Gray mapping scheme.

At step 616, the operational control flow stops.

CONCLUSION

It is to be appreciated that the Detailed Description section, and notthe Abstract section, is intended to be used to interpret the claims.The Abstract section may set forth one or more, but not all exemplaryembodiments, of the present invention, and thus, are not intended tolimit the present invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries may be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

It will be apparent to those skilled in the relevant art(s) that variouschanges in form and detail can be made therein without departing fromthe spirit and scope of the present invention. Thus, the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

1. A method to map a sequence of data into modulation symbols,comprising: (a) separating the sequence of data into a sequence ofpre-encoded data and a sequence of unencoded data; (b) encoding thesequence of pre-encoded data using a Low Density Parity Check (LDPC)Code to provide a first sequence of encoded data; (c) combining a firstbit increment from the sequence of unencoded data and a second bitincrement from the first sequence of encoded data to provide a secondsequence of encoded data; (d) segmenting the second sequence of encodeddata into a plurality of symbol labels; and (e) assigning to each symbollabel from the plurality of symbol labels a corresponding modulationsymbol from a Quadrature Amplitude Modulation (QAM) constellation inaccordance with a specific mapping scheme.
 2. The method of claim 1,prior to step (a), further comprising: (1) encoding the sequence of datausing one or more encoding algorithms.
 3. The method of claim 2, whereinstep (1) comprises: (1)(i) encoding the sequence of data using at leastone of: a first outer encoding algorithm and a first inner encodingalgorithm.
 4. The method of claim 2, wherein step (1)(i) comprises:(1)(i)(A) encoding the sequence of data using at least one of: aBose-Chaudhuri-Hocquenghem (BCH) code, a Digital VideoBroadcasting-Satellite-Second Generation Low Density Parity Check(DVB-S2 LDPC) code, and a Reed Solomon code.
 5. The method of claim 1,wherein step (b) comprises: (b)(i) encoding the sequence of pre-encodeddata using a DVB-S2 LDPC code to provide the first sequence of encodeddata.
 6. The method of claim 1, wherein step (b) comprises: (b)(i)encoding the sequence of pre-encoded data using a second outer encodingalgorithm to provide a sequence of outer encoded data; and (b)(ii)encoding the sequence of outer encoded data using the Low Density ParityCheck (LDPC) Code to provide the first sequence of encoded data.
 7. Themethod of claim 6, wherein step (b)(i) comprises: (b)(i)(A) encoding thesequence of pre-encoded data using a BCH code.
 8. The method of claim 6,wherein step (b)(ii) comprises: (b)(ii) encoding the sequence of outerencoded data the DVB-S2 LDPC code.
 9. The method of claim 1, whereinstep (b) comprises: (b)(i) encoding the sequence of pre-encoded datausing a second outer encoding algorithm to provide a sequence of outerencoded data; (b)(ii) encoding the sequence of outer encoded data usingthe Low Density Parity Check (LDPC) Code to provide a sequence of innerencoded data; and (b)(iii) interleaving the sequence of inner encodeddata to provide the first sequence of encoded data.
 10. The method ofclaim 1, wherein step (c) comprises: (c)(i) combining at least one of: afirst four-bit increment from the sequence of unencoded data and asecond four-bit increment from the first sequence of encoded data toprovide the second sequence of encoded data corresponding to modulationsymbols of a first 256-QAM constellation, a two-bit increment from thesequence of unencoded data and a six-bit increment from the firstsequence of encoded data to provide the second sequence of encoded datacorresponding to modulation symbols of a second 256-QAM constellation, afour-bit increment from the sequence of unencoded data and a six-bitincrement from the first sequence of encoded data to provide the secondsequence of encoded data corresponding to modulation symbols of a1024-QAM constellation, and a first six-bit increment from the sequenceof unencoded data and a second six-bit increment from the first sequenceof encoded data to provide the second sequence of encoded datacorresponding to modulation symbols of a 4096-QAM constellation.
 11. Themethod of claim 1, wherein step (d) comprises: (d)(i) segmenting thesecond sequence of encoded data into a plurality of bit patterns. 12.The method of claim 1, wherein step (d)(i) comprises: (d)(i)(A)segmenting the second sequence of encoded data into at least one of:four-bit patterns, five-bit patterns, and six-bit patterns.
 13. Themethod of claim 1, wherein step (e) comprises: (e)(i) assigning to eachsymbol label from the plurality of symbol labels a correspondingmodulation symbol from at least one of: a 16-QAM constellation, a 32-QAMconstellation, and a 64-QAM constellation.
 14. The method of claim 1,wherein step (e) comprises: (e)(i) assigning to each symbol label fromthe plurality of symbol labels a corresponding modulation symbol fromthe QAM constellation in accordance with a Gray mapping scheme.
 15. Anapparatus to map a sequence of data into modulation symbols, comprising:a bit splitter module configured to separate the sequence of data into asequence of pre-encoded data and a sequence of unencoded data; a firstencoding module configured to encode the sequence of pre-encoded datausing a LDPC code to provide a first sequence of encoded data; a bitcombiner module configured to combine a first bit increment from thesequence of unencoded data and a second bit increment from the firstsequence of encoded data to provide a second sequence of encoded dataand to segment the second sequence of encoded data into a plurality ofsymbol labels; and a symbol mapper configured to assign to each symbollabel from the plurality of symbol labels a corresponding modulationsymbol from a QAM constellation in accordance with a specific mappingscheme.
 16. The apparatus of claim 15, further comprising: a secondencoding module configured to encode the sequence of data using one ormore encoding algorithms.
 17. The apparatus of claim 16, wherein the oneor more encoding algorithms includes at least one of: a first outerencoding algorithm and a first inner encoding algorithm.
 18. Theapparatus of claim 16, wherein the one or more encoding algorithmsincludes at least one of: a BCH code, a DVB-S2 LDPC code, and a ReedSolomon code.
 19. The apparatus of claim 15, wherein the LDPC codeincludes a DVB-S2 LDPC code to provide the first sequence of encodeddata.
 20. The apparatus of claim 15, wherein the first encoding modulecomprises: an outer encoding module configured to encode the sequence ofpre-encoded data using a second outer encoding algorithm to provide asequence of outer encoded data; and an inner encoding module configuredto encode the sequence of outer encoded data using the LDPC Code toprovide the first sequence of encoded data.
 21. The apparatus of claim20, wherein the second outer encoding algorithm includes a BCH code. 22.The apparatus of claim 20, wherein the LDPC Code includes a DVB-S2 LDPCcode.
 23. The apparatus of claim 15, wherein the first encoding modulecomprises: an outer encoding module configured to encode the sequence ofpre-encoded data using a second outer encoding algorithm to provide asequence of outer encoded data; an inner encoding module configured toencode the sequence of outer encoded data using the LDPC Code to providea sequence of inner encoded data; and interleave module configured tointerleave the sequence of inner encoded data to provide the firstsequence of encoded data.
 24. The apparatus of claim 15, wherein the bitcombiner module is configured to combine at least one of: a firstfour-bit increment from the sequence of unencoded data and a secondfour-bit increment from the first sequence of encoded data to providethe second sequence of encoded data corresponding to modulation symbolsof a first 256-QAM constellation, a two-bit increment from the sequenceof unencoded data and a six-bit increment from the first sequence ofencoded data to provide the second sequence of encoded datacorresponding to modulation symbols of a second 256-QAM constellation, afour-bit increment from the sequence of unencoded data and a six-bitincrement from the first sequence of encoded data to provide the secondsequence of encoded data corresponding to modulation symbols of a1024-QAM constellation, and a first six-bit increment from the sequenceof unencoded data and a second six-bit increment from the first sequenceof encoded data to provide the second sequence of encoded datacorresponding to modulation symbols of a 4096-QAM constellation.
 25. Theapparatus of claim 15, wherein the bit combiner module is configured tosegment the second sequence of encoded data into a plurality of bitpatterns.
 26. The apparatus of claim 15, wherein the bit combiner moduleis configured to segment the second sequence of encoded data into atleast one of: four bit patterns, five-bit patterns, and six-bitpatterns.
 27. The apparatus of claim 15, wherein the symbol mapper isconfigured to assign to each symbol label from the plurality of symbollabels a corresponding modulation symbol from at least one of: a 16-QAMconstellation, a 32-QAM constellation, and a 64-QAM constellation. 28.The apparatus of claim 15, wherein the symbol mapper is configured toassign to each symbol label from the plurality of symbol labels acorresponding modulation symbol from the QAM constellation in accordancewith a Gray mapping scheme.